A      3>-'7 


Bulletin  No.  43. 

U.  S    DEPARTMENT   OF 

OFFICE  OF  EXPERIMENI 


LOSSES  IN  BOILING  V 


AND    TIIK 


COMPOSITION  AND   DIGESTIBILITY 
OF  POTATOES  AND  EGGS. 

u-s.  depository" 

H.  SNYDER,  B.  S.,  ALMAH  J.  FRISBY,  M.  D.,  AND  A.  P.  BRYANT,  M.  S. 


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Bulletin  No.  43. 


212. 


U.  S.  DEPARTMENT  OF  AGRICULTURE. 

OFFICE  OF  FXPERTMENT  STATIONS. 


LOSSES  l.\  BOILING  VEGETABLES 


AND    THE 


COMPOSITION  AND   DIGESTIBILITY 
OF  POTATOES  AND  EGGS. 


BY 


H.  SNYDER,  B.  S.,  ALMAH  J.  FRISBY,  M.  D.,  AND  A.  P.  BRYANT,  M.  S. 


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WASHINGTON: 

3TEENMENT    PRINTING    OFFICE, 

1897. 


LETTER  OF  TRANSMITTAL 


U.  S.  Department  of  Agriculture, 

Office  of  Experiment  Stations, 

Washington,  />.  C  May  15,   1897. 

Sir:  I  have  the  honor  to  transmit  herewith  a  report  on  the  loss  of 
nutrients  in  boiling  potatoes,  carrots,  and  cabbage,  and  the  composi- 
tion and  digestibility  of  potatoes  and  eggs,  by  Prof.  H.  Snyder,  Alinah  J. 
Frisby,  M.  I).,  and  A.  P.  Bryant,  M.  S.  These  investigations  consti- 
tute a  part  of  the  inquiries  made  with  the  funds  appropriated  by  Con- 
gress ';  to  enable  the  Secretary  of  Agriculture  to  investigate  and  report 
upon  the  nutritive  value  of  the  various  articles  and  commodities  used 
for  human  food,"  and  were  carried  on  under  the  supervision  of  Professor 
At  water,  special  ageut  in  charge  of  nutrition  investigations,  in  accord- 
ance with  instructions  given  by  the  Director  of  this  Office. 

The  greater  part  of  the  food  of  man  is  prepared  for  use  by  cooking, 
yet  the  changes  which  various  foods  undergo  during  the  process  and 
the  losse*  which  are  brought  about  by  cooking  have  been  little  studied. 
This  question  has  a  wide  practical  application  as  well  as  scientific 
interest.  In  determining  the  nutritive  value  of  various  articles  of  food, 
digestibility  is  an  important  consideration.  Perhaps  no  feature  of  the 
subject  is  more  discussed.  Nevertheless  very  few  experiments  with 
man  to  determine  the  digestibility  of  various  foods  have  been  made. 
Almost  all  information  has  been  derived  from  artificial  digestion  experi- 
ments which  approximate  more  or  less  closely  digestion  in  the  body. 
It  is  by  no  means  certain  that  the  two  processes  give  the  same  results. 
Digestion  experiments  with  man  were  believed  to  be  necessary,  and 
a  diet  in  which  potatoes  were  the  chief  ingredient  was  selected  for 
experimental  purposes. 

Professor  Snyder's  work  was  carried  on  in  the  laboratory  of  the  Col- 
lege of  Agriculture  of  the  University  of  Minnesota;  that  of  Dr.  Frisby 
and  Mr.  Bryant  in  the  chemical  laboratory  of  Wesleyan  University, 
Middletown,  Conn. 

This  report  is  respectfully  submitted,  with  the  recommendation  that 
it  be  published  as  Bulletin  No.  43  of  this  Office. 
Respectfully, 

A.  C.  True, 

Director. 

Hon.  James  Wilson, 

Secretary  of  Agriculture. 

3 


CONTENTS. 


Page. 
LOSS    OF    NUTRIENTS    IN    BOILING    POTATOES,     CARROTS,     AND     CABBAGE.      By 

II.  Snyder,  B.  S 7 

Introduction 7 

The  three  principal  classes  of  nutrients  in  foods 7 

The  effect  of  cooking  on  the  nutrients  of  foods 8 

Experiments  with  potatoes 9 

Composition  of  potatoes 9 

Cooking  tests : 11 

Discussion  of  results 13 

Conclusions 14 

Experiments  with  carrots 15 

Composition  of  carrots 15 

Cooking  tests 15 

Conclusions 17 

Experiments  with  cabbage 17 

Composition  of  cabbage 17 

Cooking  tests 18 

Conclusions 19 

General  summary 19 

The  digestibility  of  potatoes  and  eggs.     By  H.  Snyder,  B.  S 20 

Introduction 20 

Digestibility  of  boiled  eggs  in  pepsin  solution 20 

Digestion  experiment  on  man  with  a  diet  of  potatoes,  eggs,  milk,  and 

cream ^ 21 

Discussion  of  results 23 

The  composition  of  different  parts  of  the  potato  and  the  loss  of 
nutrients  during  the  process  of  boiling.     By  Almah  J.  Frisby,  M.  D., 

and  A.  P.  Bryant,  M.  S 25 

Introduction 25 

Composition  of  different  parts  of  the  potato 26 

Sampling 26 

The  analyses 27 

The  protein  factor 28 

Amount  of  solid  matter  in  the  j  uice  of  the  potato 29 

Loss  of  nutrienvs  in  boiling 29 

Conclusions 31 

5 


ILLUSTRATIONS. 


Fig.  1.  Cells  of  a  raw  potato  with  starch  grains  in  natural  condition 8 

2.  Cells  of  a  partially  cooked  potato 8 

3.  Cells  of  a  thoroughly  boiled  potato !» 

4.  The  composition  of  the  potato  and  the  loss  of  nutrients  when  boiled 

with  the  skin  removed 14 

5.  The  composil  ion  of  the  carrot  and  the  loss  of  nutrients  when  boiled..  17 
(>.  The  composition  of  the  cabbage  and  the  loss  of  nutrients  when  boiled.  lit 
7.  Transverse  and  longitudinal  sections  of  the  potato 2."> 

6 


iS  IN  BOILING  VEGETABLES,  AND  THE  COMPOSITION 
AND  DIGESTIBILITY  OF  POTATOES  AND  EGGS. 


LOSS  OF  NUTRIENTS  IN  BOILING  POTATOES,  CARROTS,  AND 

CABBAGE. 

By  II.  Snyder,  B.  >.. 

Chemist,  Minnesota  Agricultural  Experiment  Station,  and  Professor  of  Agricultural 

Chemistry,  College  of  Agriculture,  University  of  Minnesota. 

INTRODUCTION. 

Tin:   THREE    PRINCIPAL   CLASSES   OF   NUTRIENTS   IN   FOODS. 

The  nutritive  ingredients  of  foods  are  commonly  divided  into  three 
general  classes,  namely,  nitrogenous  substances  to  which  the  general 
term  protein  is  applied,  fats,  and  carbohydrates. 

The  nitrogenous  substances.- — The  nitrogenous  substances  include  (1) 
the  albuminoids,  of  which  egg  albumen  is  a  well-known  example;  (2)  the 
so-called  gelatinoids,  of  which  gelatin  may  serve  as  a  type;  and  (3) 
the  amids;  i.  e.,  synthesis  and  cleavage  products  of  various  kinds. 

The  vegetable  albuminoids  are  to  a  large  extent  different  from 
those  found  in  animal  foods.  They  appear  to  be  more  variable  in 
composition,  and  less  is  known  concerning  their  chemical  composi- 
tion, structure,  and  digestibility. 

The  fats. — The  amount  of  dry  matter  dissolved  out  of  a  substance  by 
continuous  treatment  with  ether  is  designated  as  fat.  It  forms  a  large 
part  of  animal  foods,  but  iu  vegetable  foods,  with  the  exception  of  some 
seeds  and  nuts,  the  proportion  is  very  small. 

The  carbohydrates. — This  class  includes  the  sugars,  starches,  woody 
fibers,  cell  walls,  etc.,  of  the  vegetable  foods.  Carbohydrates  are  found, 
in  but  few  animal  foods,  with  the  exception  of  milk,  and  when  present 
are  in  very  small  quantities.  In  vegetable  foods,  on  the  contrary,  they 
form  the  major  part  of  the  nutritive  matter.  The  principal  constituent 
of  vegetable  carbohydrates  is  starch.  The  starch  grains  are  usually 
inclosed  in  thin  cells,  the  walls  of  which  may  be  composed  of  more  or 
less  fibrous  material. 

The  digestibility  of  the  carbohydrates  depends  upon  the  proportion 
of  sugar  and  starches  to  cell  walls  or  fiber.  The  sugars  are  more  easily 
digested  than  the  starches,  since  the  latter  must  be  changed  to  sugar  in 
the  process  of  digestion  before  it  can  be  assimilated  by  the  body.     Both 

7 


- 


Fig.  i 


»t  a  r.iw  ].<.t.ito  with 
condition. 


itarcb  u  1:1111-  in  natural 


the  starches  and  the  sugars,  bowe*  er,  are  probably  completely  digested, 
bin   the  cell  walls,  the  framework  of  the  substance,  are  not  so  easily 
ted  :  in  fact,  while  98  to  1<»<>  per  cciii  of  the  starches  and  su£ 

may  be  digested,  the  di_ 
ibility  of  these  cell  walls,  01 
fiber  as  it  is  called,  may  vary 
all  the  way  from  30  to  7u  per 
cent 

1  Hi:    1:1  ri.i   l    01     «  « POKING    « ».\     l  111. 
\  1    1  1:11  \  1  -    OJ     1  « •• 

Borne  of  the  albuminoids 
Soluble  in  water,  ami 
nearly  all  in  dilute  saline 
solutions.  II  eat  i  ng  coagu- 
lates the  albuminoids  and 
renders  them  insoluble. 
<  looking,  therefore,  preserves 
albuminoids  from  I088,  It 
meat  is  put  into  cold  water 
and  then  brought  to  the  boil 
in*:  point  more  or  less  of  the 
albuminoid  material  will  be  dissolved  and  some  of  the  most  expensive 
part  of  the  food  will  be  lost  unless  the  soup  is  utilized  also.  If  put 
directly  into  hot  or  boiling  water  the  soluble  albuminoids  on  the  surface 
will  be  coagulated,  and  this 
loss  will  be  largely  pre 
vented.1  The  same  princi- 
ple is  probably  applicable 
to  vegetables  also. 

Besides  rendering  sol- 
uble albuminoids  insoluble, 
cooking  makes  others  of 
the  nitrogenous  substances 
more  digestible,  and  in  the 
case  of  meats  loosens  the 
libers  of  connective  tissue, 
rendering  it  tender  and 
more  palatable.  Unless  the 
degree  of  heat  is  great 
enough  to  cause  scorching, 
fats  arc  doubtless  little  af- 
fected by  cooking. 

The  carbohydrates  are 
much  more  easily  digested  in  the  cooked  than  in  the  raw  state.     In  the 
raw  food  the  sugars  and  starches  are  inclosed  in  cells.     Very  little  of 


r.  S.  Dept  A_i..  Farmers'  Bui. 34. 


the  cellulose  of  the  cell  walls  is  digested  by  man.  The  cell  contents, 
therefore,  are  often  excreted  unchanged.  Cooking  bursts  these  cell 
walls,  thus  exposing  the  inclosed  sugars  and  st;n dies  to  the  action  of 
the  digestive  juices.  The  starch  granules  also  swell  up  and  burst  on 
cooking,  exposing  more  surface  to  be  acted  upon.  Starch  is  to  a  slight 
extent  changed  to  dextrin  by  dry  heat,  and  possibly,  also,  by  heating 
with  water.  Since  the  majority  of  vegetable  foods,  however,  consist 
largely  of  starches  and 
have  very  little  sugar  in 
them,  the  loss  of  carbohy- 
drates would  presumably 
not  be  very  great  during 
boiling. 

The  effect  of  boiling  upon 
the  cells  of  the  potato  is 
shown  in  figs.  1,  2,  and  3.1 

Several  years  ago  Kath. 
erine  Williams  reported2 
an  extended  study  of  the 
composition  of  a  number  of 
cooked  and  a  few  raw  vege- 
tables. Ultimate  and  prox- 
imate analyses  of  the  vari- 
ous vegetables  were  made 
and  the  fuel  value  deter- 
mined. Many  cooked  veg- 
etables have  been  analyzed  in  connection  with  the  food  investigations 
undertaken  by  this  Department  and  by  other  investigators. 

Comparatively  few  attempts  have  been  made  to  learn  the  changes 
which  take  place  in  vegetable  foods  on  cooking,  or  the  extent  of  these 
changes.  As  the  water  in  which  vegetables  are  boiled  is  usually  thrown 
away,  any  matter  which  was  in  solution  would  be  Avasted.  Experiments 
were  therefore  undertaken  with  potatoes,  carrots,  and  cabbage  for  the 
purpose  of  studying  the  loss  of  nutrients  when  boiled,  under  a  number 
of  different  conditions.  These  vegetables  were  selected  as  the  best 
representatives  of  tubers,  roots,  and  pot  herbs. 

EXPERIMENTS   WITH   POTATOES. 
COMPOSITION   OF   POTATOES. 

According  to  Lawes  and  Gilbert,3  the  composition  of  the  flesh  of  the 
potato  differs  from  that  of  the  juice.  Although  the  flesh  contains  85 
per  cent  of  the  total  water  free  substance,  it  contains  but  15  per  cent  of 

1 U.  S.  Dept.  Agr.,  Office  of  Experiment  Stations  Bui.  21,  p.  88 ;  from  Miirckers  Stu- 
dien  in  der  Spiritusfabrikation. 

2  Jour.  Chem.  Soc.  [Loudon],  61  (1892),  p.  226. 

3  "On  the  growth  of  the  potato,*'  p.  26,  Kotliamsted  Memoirs,  vol.  6. 


Cells  of  :i  thoroughly  boiled  potato. 


10 


tin'  nitrogen.  The  remainder,  85  per  cent,  is  in  the  juice.  Of  this  49 
percent  is  in  the  form  of  albuminoid  and  36  per  cent  in  the  form  of 
nonalbuminoid  mi rogen. 

The  proportion  of  albuminoid  and  nonalbuminoid  nitrogen  varies 
greatly  according  to  different  writers.  E.  Schulze  and  Barbieri'and 
B.  Schulze  and  B.  Bugster  give,  as  the  result  of  five  analyses,  from  35 
to  56  percent  of  nonalbuminoid  nitrogen.  0.  Kellner  gives  ii  to 58 
percent  of  nonalbuminoid  nitrogen,  and  A.  Bforgen  from  30  to  52  per 
cent,  making  l~>  per  cent  as  a  lair  average  of  the  amount  of  nonal 
buminoid  nitrogeu  and  55  per  cent  for  the  amount  of  albuminoid  nitro- 
gen present  in  potatoes.  In  the  experiments  here  reported  the  figures 
obtained  were  nearly  the  reverse  of  these  latter,  as  the  average  of  the 
two  analyses  made  gasve  40  per  cent  of  albuminoid  and  60  per  cent  of 
nonalbuminoid  nitrogen  (see  also  p.  29).  [t  is  evident  that  in  boiling 
the  loss  of  a  considerable  portion  of  this  albuminoid  nitrogen  may 
occur. 

There  is  also  a  possibility  of  loss  of  inorganic  and  organic  salts  dur- 
ing cooking.  Probably  about  85  per  cent  of  the  potash  of  the  potato, 
as  well  as  the  larger  part  of  the  citric  acid,  is  in  the  juice.  The  total 
amount  of  citric  acid,  however,  is  small.  While  potash  salts  and  cit- 
rates have  no  real  nutritive  value,  t  hey  appear  to  be  <>f  some  considerable 
medicinal  or  tonic  value  and  give  *•  relish"  to  the  food.  No  attempt  was 
made  to  determine  the  loss  of  fat  and  liber  in  boiling.  It  would  be 
presumably,  very  small. 

Three  experiment  sou  the  effect  of  cooking  on  the  composition  of  pota- 
toes were  made.  In  the  first  experiment  (A)  the  skins  were  removed  and. 
the  potatoes  soaked  three  and  five  hours,  respectively,  and  cooked  in 
distilled  water,  which  was  cold  at  the  beginning  of  the  test.  In  the 
second  experiment  (B)  the  skins  were  removed  and  the  potatoes,  with- 
out previous  soaking,  were  cooked  in  (1)  distilled  water  (soft  water), 
(2)  alkaline  water,  (3)  limewater  (hard  water),  which  was  in  each  case 
cold  at  the  beginning;  in  (4)  distilled  water,  (5)  alkaline  water, and  (<>) 
limewater,  which  was  in  each  case  hot  at  the  beginning  of  the  test. 
In  the  third  experiment  (0)  the  potatoes  were  not  peeled  and  were 
cooked  without  previous  soaking  in  distilled,  alkaline,  and  limewater, 
which  was  cold  at  the  beginning  of  the  test,  and  in  distilled,  alkaline, 
and  limewater,  which  was  hot  at  the  beginning  of  the  test. 

About  two  bushels  of  potatoes  of  a  uniform  character  were  divided 
into  lots  of  about  a  kilogram  (2£  pounds)  each.  An  analysis  was  made 
of  the  whole  potato,  including  the  skin.  This  was  assumed  to  repre- 
sent the  composition  of  all  the  potatoes  used  in  the  experiments  except 
those  which  were  soaked  before  boiling.     In  this  latter  case  half  of  each 


1  Landw.  Vera.  Stat.,  21  |  L878),  i».  63, 
"Ibid.,  27    L882  .  p.  :;:>7. 
Konig,  Chemi<  der  menschlichen  Nahrangs-  and* tanussmittel,  3ded.,  [I, p. 631. 


11 

of  the  peeled  potatoes  used  in  the  experiment  was  taken  as  a  sample 
and  analyzed. 

The  methods  of  analysis  used  were  substantially  those  adopted  by 
the  Association  of  Official  Agricultural  Chemists, and  were  as  follows: 

Nitrogen. — In  order  to  ascertain  the  relative  proportion  of  albumi- 
noids and  extractives  or  ainids  the  nitrogen  was  determined,  (1)  as  the 
total  nitrogen  by  the  Kjeldahl  method,  and  (2)  the  albuminoid  nitrogen 
by  the  Stutzer  method.  The  results  for  albuminoid  nitrogen  are  with- 
out doubt  too  low,  as  the  copper  proteid  dissolved  to  a  slight  extent  in 
the  moderately  warm  solution  when  filtered  and  separated  out  on  stand- 
ing. If  filtered  when  cold  the  filtration  was  so  slow  that  fermentation, 
with  a  consequent  loss  of  the  copper  proteid,  would  begin  before  the 
filtration  was  completed. 

Starch. — Starch  was  determined  by  inversion  with  boiling  hydro- 
chloric acid  and  water  and  estimating  the  amount  of  copper  in  Fehliug's 
solution  precipitated  by  the  resulting  dextrin. 

Fat,  fiber,  and  ash. — These  were  determined  in  the  usual  way  in  the 
fresh  material. 

The  accompanying  table  shows  the  composition  of  the  potatoes  used 
in  these  experiments,  and  gives  also  the  composition  as  obtained  by 
former  analyses  at  the  University  of  Minnesota,1  the  average  of  all 
American  analyses,2  and  the  average  of  European  analyses.3 

Composition  of  potatoes'. 


Num- 
ber of 

analy- 
ses." 

Fat. 

Carbohydrates. 

Water    minoid 
water-     nitro- 

1    gen. 

Total 
nitro 
gen. 

Pro- 
tein. 

Fiber. 

Starch. 

Nitro- 
gen- 
free  ex- 
tract, a 

Ash. 

Used    in   Experi- 

1 

Per  ct. 
78  n 

Per  ct. 

0.15 

.15 
.20 

Per  ct. 
0.35 

.40 
.40 

Per  ct. 
2.2 

2.5 

2.5 
2.2 
2.1 

Per  ct. 

Pet  ct. 

Per  ct. 

J'er  ct. 

Per  ct. 
0.9 

Used    in     Eperi- 
ments  F>  and  C. 

Average       other 
Minnesota  anal 

1         77.2 
20          75. 5 

0.1 

.1 
.1 
.1 

0.2 
.3 

16.4 
19.9 

19.3 

20.9 
18.8 
21.7 

.9 
1.0 

Average  all  Anier- 

86          78. 0 

.9 

Average       Euro- 
pean analyses  . . 

178 

75.  0 

&.19 

.34 

.7 

1.1 

a  100  less  the  sum  of  the  percentages  of  water,  protein,  fat,  and  ash. 
b Calculated,  allowing  45  per  cent  to  be  albuminoid. 

COOKING   TESTS. 

The  potatoes  were  boiled  in  a  metal  kettle  over  a  gas  flame  at 
about  the  same  rate  as  when  cooked  in  the  kitchen.  The  uncooked 
potatoes  were  weighed,  and  the  water  in  which  they  were  cooked  was 
also  weighed  and  analyzed.  The  total  amounts  of  dry  matter,  albumi- 
noid nitrogen,  total  nitrogen,  starch,  and  ash  that  were  removed  in 


1  Minnesota  Sta.  Bui.  42. 

2  From  an  unpublished  compilation  of  analyses  of  American  food  products. 
3Konig,  Chemie  der  menschlichen  Nahrungs-  mid  Gennssmittel,  3d  ed.,  II,  p.  626. 


12 

cooking  i<><>  parts  of  fresh  potatoes  was  then  calculated.    The  results 
of  each  of  the  three  experiments  are  given  In  the  following  tabic: 


matU  r  in  <  nnhtinj  potatoe*. 


|i 

(,,<IIIIS 

eo9 

of  mattei  In 

pot.,' 

Mtltll.   lit. 

roll 

Method  of  preparation  and 
Booking. 

1 

1 

a 

If 

"3  = 

-  5 

— 

- 

i 

A 

i 

a 

= 

u 

- 

h 

IE.TZ 

<-- 

6 

l 

- 

m 
4 

h>f    •■■•kiwi. 

Boaked    3    bonre;     distilled 
water,  oold  at  star! 

Boaked     5     boura;     distilled 
w  ater,  oold  at  atari  

I'.ct. 

L45 
1.40 

I'.ct. 
.040 

/  .< 

0  I'd 

i'.ct. 

0.41 
.28 

I'.ct. 
6.4 

r.,t 

26.7 

57.7 

I'.ct. 

r.c,. 

45.  6 
31.1 

1.43 

.038 

.181    

.35 

6.5 

25.0 

51.8 

38  3 

B.  Skint                 not  toahed. 

Distilled  water,  oold  a1 

I),,    

MS 
939 

.63 

.7-4 

.mm; 

.006 

.055 
.080 

0.16 
.16 

.18 
.15 

2.8 

3.2 

4.7 
4.0 

13.8 

•'II    n 

1.0 

1.0 

19.6 
16.3 



.68 

.006 

.068 

.16 

.16 

3.0 

4.3      16.9 

1.0 

17.0 

Alkaline  water,  cold  at  Btari 
Do 

1.  L65 
952 

.68 

.67 

.016 
.011 

.055 
.061 

.15 

.19 

.17 

.17 

3.0 

10.7 

16.7 

.9 
1.2 

18.  5 
18.5 

.67 

.014 

.065 

.17 

.17 

2.9 

9.  0     15.  2 

1.0 

18.5 

Limewater,  cold  at  start 

Do 

907 

.70 
.79 

.011 
.  015 

.055 

.067 

.14 
.17 

.18 

.19 

3.1 
3.5 

7.3      13.8 
10.0      16.7 

,-9 
1.0 

2H.6 

Average 



.75 

.o\:; 

.061 

.16 

.19 

3.3 

9.0      15.3 

1.0 

20.1 

A\  erage  of  6  test>  start 

3.1 

7.3 

1.0 

18.8 



Distilled  water,  hot  at  start. . 
Do 

939 
1,052 

.72 
.52 

'.'ooi' 

.033 
.027 

.11 
.10 

.17 
.08 

3.2 

2.3 

1     8.2 

2.  7       »;.  7 

.  7 
.6 

18.5 
8.7 

Average 

.62 

.004     .025 

.10 

.13 

2.8 

2.  7        7.  5 

•6 

10 

1.2 

13.6 

Alkaline  water,  hot  at  start.. 
Do 

988 
970 

.71 

.80 

.003 

.004 

.033 
.041 

.17 
.19 

.19 

.  22 

3.1 
3.5 

2.0 

2.7 

8.3 
10.2 

20.7 
23.9 

.76 

.  003      .  037 

.18 

.21 

3.3 

2.  3        9.  2 

1.  1 

22.3 

Limewater,  hot  at  start 

Do 

1,043 

1.15 

.78 

.024 
.007      .038 

.26 
.17 

.15 
.19 

5.1 

3.4 

4.0  I     6.0 

4.7        9.5 

1.6 

1.0 

16.3 

Average 



.96 

.006 

.031 

.22 

.17 

4.2 

4.3  |     7.8 

13 

18.5 

A  verage  of8  tests  start- 

3.4 

3.2 

1.0 

18.1 

<m:\ 
952 

.14 

.  11 

<      SJ  <"/'»■  not  '■'  morn  <t. 

Distilled  water,  cold  at  start 

Do 

Trace 

Trace 

.005 
.004 

.03 
.07 

.6 
.5 

.3        1.2 
.1        1.0 

3.3 
7.6 

\  rerage 

1,034 

.13 

- 
.12 

Trace 

Trace 
Trace 

.005 

.05 

.6 

.2  1    1.1 

5.4 

Alkaline  water,  cold  at  >tat  t 
Do 

.004 

.005 

.03 

.04 

:i 

.3        1.0 

1    2 



3.3 
4.3 

.10 

Trace    .005 

.04 

•5 

.3        1.1 

3.8 

Limewater,  cold  at  start 

Do 

1,474 

.04 

.  002     .  003 

.  002      . 003 



.01 

•2 

L8 

.7 
.8 

.1 

.1 

1.1 

.04 

.002      .003 

.01 

2 

1.3  |      .8 

.  1 

1.1 

A\  erage  of  6  test-  start- 

.4 

.6 

1.0 

.1 

3  4 

..    .,    .'..     .. 

13 


Loss  of  matter  in  cooking  potatoes— Continued. 


1 

2 

a 
o    . 

'—    0> 

O  m 

•a  P 

ho 
"3 

Loss  of  matter  in  fresh 

potatoes. 

Percentage  Lose  of  each  con 

-1  it  mnt . 

Method  of  preparation  and 

2 
Q 

1  a 

"=   if. 

§   O 

2 

'3  d 

_  ^ 

o 
H 

4 

C 

5 

-a 

"§  d 

5  s 
-  u 

5 

E 

'3  d 

—  - 
%  -i 

e 
- 

-d 
3 

3 

0Q 

.d 

4 

C.  Skins  not  removed  -Cont'd. 

Distilled  water,  hot  at  start.. 
Do 

Oramt. 

1,047 

1,075 

P.et. 

0.  15 
.10 

J'.ct. 

0.001 

.001 

0.  005 
.  008 

r.ct. 

P.et. 

0.05 
.04 

P.et. 

0.7 
.7 

o.  5 
.  5 

P.et. 

1.3 
2.0 

/'.-•/. 

P.et. 

5.4 
4.4 

.16 

.001 

.006 

.05 

.7 

.5 

1.6 

4.9 

Alkaline  water,  hot  at  start. . 
Do 

1,229 
1,034 

.10 
.09 

trace, 
trace. 

.  003 
.003 

.03 

.02 

.4 

.4 

■ 

.2 
.2 

.8 



3.1j 
2.2 

.10 

trace. 

.003 

03 

.4 

.2 

.8 

2.7 

Liruewater,  hot  at  start 

Do 

1,075 
848 

.04 

.06 

.001 

.001 

.002 
.003 

0.01 
.01 

.02 

.02 

.2 
.3 

.4 
.5 

.5 

0.1 

.  1 

2.2 
2.2 

.05 

.001 

.002 

.01 

.02 

.2 

.5  :       .7         .1 

2.2 

Average  of  6  tests  start- 

.4 

.4 

1.0 

.1 

3.3 

The  weight  of  each  ingredient  removed  divided  by  the  total  weight 
of  the  same  ingredient  in  the  fresh  potatoes  before  cooking  gives  the 
percentage  of  loss  of  tbat  substance.  These  figures  are  shown  in  the 
last  five  columns  of  the  table.  The  same  composition  was  assumed  for 
the  peeled  potatoes  used  in  Experiment  B  as  for  the  whole  potatoes 
used  in  Experiment  O.  This  may  not  be  strictly  accurate,  since  it  pre- 
supposes the  uniform  composition  of  all  parts  of  the  potato.  As  shown 
on  page  27,  there  is  a  slight  variation  between  the  composition  of  the 
interior  and  the  part  peeled  off,  but  this  probably  is  not  great  enough 
to  have  a  material  effect  upon  the  results  obtained. 


DISCUSSION   OF   RESULTS. 

By  reference  to  the  table  (p.  12)  it  will  be  seen  that,  as  might  be 
expected,  the  greatest  loss  occurs  when  the  potatoes  are  peeled  and 
soaked  in  cold  water  before  boiling.  In  this  case  the  loss  of  nitroge- 
nous matter  was  from  46  to  58  per  cent,  depending  upon  the  length  of 
time  they  were  soaked.  Of  the  albuminoids  25  per  cent  and  of  the 
mineral  matters  38  per  cent  were  extracted  by  the  water  in  which  the 
potatoes  were  cooked.  The  water  would  ordinarily  be  thrown  away 
and  this  material  lost. 

When  the  potatoes  are  peeled  and  put  into  cold  water,  and  heated 
to  boiling  as  soon  as  possible,  the  loss  is  much  smaller,  being  about  16 
per  cent  of  the  total  nitrogenous  matter  (of  which  albuminoids  form  a 
trifle  less  than  half)  and  about  19  per  cent  of  the  total  mineral  matter. 
When  the  potatoes  are  peeled  and  put  directly  into  boiling  water  the 
loss  of  albuminoid  and  other  nitrogenous  matter  is  only  about  half 
that  of  the  last  case,  but  the  amount  of  mineral  matter  is  practically 


14 

the  same.    The  boiling  water  booh  coagulates  the  albuminoids  on  the 

surface  of  the  potato,  rendering  them  Insoluble.  They  till  the  outer 
pores  of  the  potato,  rendering  the  inner  juice-  Less  liable  to  loss,  although 
Dot  before  a  considerable  amount  of  the  salts  or  mineral  matter  bas 
escaped.    The  relative  amount  of  oonalbuminoid  nitrogen  lost  is  greater 

than  when   the   potatoes  are   put    into  cold  watei   at    the  start.     There 

seemed  to  be  bu1  little  difference  as  regards  total  nitrogenous  matter, 

starch,  and    ash,  whether   distilled,   alkaline,   or    limewater   was  used. 

Tin-  limewater,  however,  seemed  to  have  a  greater  solvent  action  upon 

the  albuminoids  than  did  the  distilled  OI  alkaline  waters.  The  solvent 
action  of  cold  alkaline  water  was  somewhat  greater  than  that  of  dis- 
tilled water.  Inasmuch  as  the  albuminoid  material  of  the  potato  18  a 
globulin,1  and  globulins  are  insoluble  in  pure  w  atei  hut  soluble  in  saline 
water,  this  also  is  w  hat  would  be  expected.  The  salts  in  solution  in  the 
juice  of  the  potato  doubtless  carry  the  globulin  in  solution  to  some 
extent,  thus  rendering  a  loss  possible  even  in  pure  distilled  water. 
The  loss  in  boiling  peeled  potatoes  is  shown  in  graphic  form  in  figured 


FlO.  4.— The  composition  of  the  potato  and  the  1<>>s  of  nutrients  when  boiled  with  the  -kin 
removed:  a,  fiber,  pectoee,  fat,etc.;  b.  nonalbmnmoid  nitrogenous  matter;  <■.  albuminoid  nitrogenous 
matter:  <l.  mineral  matter.     The  hatched  portion  represents  the  Loss. 

It  will  be  seen  from  the  table  that  when  the  potatoes  are  impeded 
the  loss  of  matter  is  very  inconsiderable,  less  than  1  per  cent  of  the 
albuminoid  matter,  only  1  per  cent  of  the  total  nitrogenous  matter, 
hardly  a  trace  of  starch,  and  but  a  little  over  :\  percent  of  the  mineral 
matter  being  extracted.  The  different  kinds  of  water  had  no  effect 
except  on  mineral  matter.  This  was  removed  to  a  greater  extent  by 
the  distilled  water  than  by  the  alkaline  or  limewater. 


LU8I0N8. 

The  conclusions  drawn  from  these  experiments  may  be  briefly  sum- 
marized as  follows: 

(1)  In  order  to  obtain  the  highest  food  value,  potatoes  should  not  be 
peeled  before  cooking. 

(2)  When  the  potatoes  are  peeled  before  cooking,  the  least  loss  IS 
sustained  by  putting  them  directly  into  hot  water  and  boiling  as  rap- 
idly as  possible.     Even  then  the  Loss  is  very  considerable. 


Qsborne  and  Campbell,  Connecticut  Mate  Sta.  Rpt  L895,  p. 21  -    l;..  B,  p.371  '• 


15 

(3)  If  potatoes  are  peeled  and  soaked  in  cold  water  before  boiling 
the  loss  of  nutrients  is  very  great,  being  one  fourth  of  all  the  albuminoid 
matter.  In  a  bushel  of  potatoes  the  loss  would  be  equivalent  to  a 
pound  of  sirloin  steak. 

EXPERIMENTS  WITH   CARROTS. 

A  series  of  experiments  similar  to  those  just  described  was  under- 
taken with  carrots.  They  were  selected  as  fairly  representative  of  the 
roots  used  for  food.  While  in  uncooked  x>otatoes  there  is  but  a  trace 
of  sugar,  such  roots  as  beets,  carrots,  parsnips,  etc.,  contain  a  con- 
siderable amount.  This  renders  it  probable  at  the  outset  that  the 
loss  in  the  cooking  of  carrots  would  be  greater  than  in  the  cooking  of 
potatoes. 

COMPOSITION    OF   CARROTS. 

Samples  of  the  carrots  used  in  the  experiments  were  analyzed.  The 
results  of  these  analyses,  as  well  as  the  average  composition  of  carrots, 
including  both  American  and  European  analyses,  are  shown  in  the 
following  table: 

Composition  of  carrots. 


2 

'5 

S 

Carbohydrates. 

r*l 

is 

a 

to 
o 
u 

a 

to 
pi 

05 

u 

OS 

be 

o    . 
u  o 

■s- 

2~ 

IS 

3 

© 

."£ 

ft* 

'3  h 

-O 

o 

a 

s 

—  - 

* 

u 

S3 

o 

< 

H 

P4 

h 

o 

Ph 

rH 

c 

H 

^ 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.ct. 

P.  ct.    P.  ct. 

P.  c£.    /'.  ct. 

P.  ct. 

Carrots  used  in  experiments  . . . 

87.5 

0.08 

0.18 

1.1 

(b) 

3.6 

3.  0       (b) 

4.0    clO.  6 

0.8 

Average  17  American  analyses  d 

88.2 

1.1 

0.4 

9.2 

1.1 

Average  35  European  analyses  e 

86.8 

1.2 

.3 

2.1 

4.1      1.5      an 

1.0 

a  100  less  the  sum  of  the  percentages  of  water,  protein,  fat,  and  ash. 

fcNot  determined. 

c  Includes  fat. 

dTJ.  S.  Dept.  Agr.,  Office  of  Experiment  Stations  Bui.  28. 

eKonig,  Chemie  der  menschlichen  Nahrungs-  und  Genussmittel,  3d  ed.,  11,  p.  649. 

Although  carrots  contain  less  nitrogen  than  potatoes,  they  seem  to 
contain  relatively  more  albuminoid  nitrogen  and  therefore  to  furnish 
more  matter  available  for  building  muscular  tissue.  In  the  carrots  used 
in  the  following  experiments,  44.4  per  cent  of  the  total  nitrogen  was  in 
the  albuminoid  form. 

COOKING  TESTS. 

In  preparing  carrots  (sliced  or  whole)  for  the  table  they  are  put  into 
either  hot  or  cold  water  and  boiled  until  they  are  soft  enough  to  be 
easily  pierced  with  a  fork.  The  water  in  which  the  carrots  have  been 
boiled  is  usually  drained  off  and  thrown  away.  Tin's  water  is  colored 
yellow  and  has  a  very  sweet  taste,  plainly  indicating  that  some  of  the 
sugar  has  been  extracted  and  lost. 

In  order  to  determine  how  much  food  value  was  lost  in  boiling  car- 


1G 


rots  under  various  conditions,  twelve  trials  wen*  made  in  which  lime- 
water  (hard  water),  alkaline  water,  and  distilled  water  (soft  water) 
were  used.  The  carrots  were  prepared  for  cooking  in  the  usual  way  by 
washing  with  a  brush,  scraping,  drying  quickly  with  a  towel,  and  cut- 
tin-  Into  pieces.  These  pieces  were  wedge-shaped,  usually  about  i 
inches  Long,  and  with  three  sides  and  a  triangular  base  measuring 
about  L J  inches  on  a  side.  In  someofthe  trials  the  pieces  were  cut 
smaller  and  in  some  larger  in  order  to  determine  the  effect  of  size  on 

the  loss  of  material.      As   in   t  he  experiments  witli    potatoes,  the  water 

in  which  the  carrots  were  cooked  was  hot  at  the  beginning  of  the  cook- 

ing  period  in  some  of  the  tests  and  cold  in  others.  The  carrots  were 
boiled  in  a  metal  kettle  over  a  gas  (lame  under  as  nearly  the  usual 
conditions  as   possible      The   loss  of  matter  in   cooking   100    parts   of 

fresh  carrots  and  the  percentages  of  each  constituent  lost  in  cooking 

under  the  various  conditions  are  shown  in  the  following  table: 
Lots  of  matter  m  cooking  oarroU. 


1 

c 

u 

u 

LoBB  Of  matter  in  l're-li 

carrots. 

Qtage  lOM  of  each  eon- 
stitnent. 

Method  of  preparation  and 
cooking. 

-  7 

-  - 
Tr 
"T 

* 

- 

r. 
B 

>. 
=- 

- 

=  E 

6 

"3   EJ 

„  - 

1 

-. 

Ee 

a 

< 

•- 
- 

B 

u" 

n 

"3  a 

=  - 
■~  u 

<-- 

=  = 
1 

--1 
= 

i     SmcM  pieces. 

Alkaline  water,  hot  at  start .. 

1. i it ir water,  lint  at  start 

Distilled  water,  OOld  at  start  . . 

Limewater,  cold  at  start 

Grams. 

349 

399 
476 

I'.rl. 

3.81 
3.55 
3.  93 

r.rt. 

0.000 
.008 
.  009 
.010 

r.rt. 

0.063 

.uTs 
.064 
.101 

I'.rt. 

•J.  IS 

1.14 

'i.~82* 

P.ct. 

0.31 
.37 
.31 
.43 

l'.rt. 
29.4 
30.5 
28.4 
31.4 

l'.rt. 

7.5 

10.0 
11.3 
12.5 

l'.rt. 
35.0 
43.3 
35.  6 
56.1 

I'.rt. 
17.3 
27.6" 

l'.rt. 
41.3 
49.4 
41.3 
57.3 

3. 74      .  008 

.077 

1.71 

.36 

29.9 

10.3     42.5     26.0 

47.3 

494 

480 
444 
353 
580 
603 
403 

/;.  Medium-sized  j'lcces. 

Distilled  water,  lint  at  stai  t .. 
Do 

2.93     .006 
3.70       006 

.048 

.1147 

.12     23.4 
.  30     29.  6 

7.:»     26.7    

7. 5      26.  1     

16.0 
40.0 

Limewater,  hot  at  start 

Alkaline  water,  lint  at  start.. 

Distilled  water,  cold  at  start.. 

Alkaline  water,  cold  at  start.. 

Do 

2  712 
•_'.  52 
2.  68 

'J.  47 

::.  61 

.005 

.006 
.005 
.005 
.003 

.055    

.045      1.58 

.050    

.047    

.055      1.92 

.34      21.7       6.3     30.6    

.33     20.2       7.5     25.0 

.15      21.4        6.2      27.8    

.29     19.8       6.3     26.1    

.43     28.9       ::.  7     30.6     29.1 

4:..  a 
44.0 
20.0 

37.3 

2,  95 

.005     .050     1.75 

.28      23.5        6.4      27.5     26.5 

37. 3 

0.   Larger 
Limewater.  oold  at  start 

499 

2.  52 

.004     .036     1.02 

.22     20.2       .">.  ii     20.0      15.5 

29.  3 

As  will  be  seen,  the  character  of  the  water  makes  little  apparent 
difference  in  the  amount  of  nutrients  lost  when  carrots  arc  boiled.  The 
loss  depends  almost  wholly  upon  the  size  of  the  pieces.  The  loss  of 
mineral  matter  is  Large,  being  nearly  one  half  of  the  total  amount 
in  the  case  of  the  small  pieces,  and  nearly  one-third  of  the  total  when 
the  pieces  were  large.  The  loss  of  nitrogenous  matter  and  sugar  is 
also  very  Large.  With  small  pieces  about  40  per  cent  of  the  total 
aitrogen  and  26  percent  of  the  total  sugar  is  Lost,  or  about  l  pound 
of  sugar  in  a  bushel  of  carrots.     With  medium  sized  pieces  the  loss  of 


17 


nitrogen  is  27  per  cent  and  of  sugar  26  per  cent.    With  large  pieces 

the  loss  of  nitrogen  is  20  per  cent  and  of  sugar  l.~>  percent.    This  latter 

loss  is  equivalent  to  over  half  a  pound  of  sugar  in  a  bushel  of  carrots. 

Of  the  total  nutrients  30  per  cent  is  lost  from  the 

small  pieces,  24  per  cenl  from  the  medium,  and  20 

percent  from  the  large  pieces.      In  other  words,  as 

ordinarily  cooked  carrots  lose  one-quarter  of  their 

nutritive  value.   Figure.")  shows  these  losses  graph 

ically. 

CONCLUSIONS. 

These  trials  suggest  that  in  order  to  retain  the 
greatest  amount  of  nutrients  in  the  cooking  of 
carrots  (1)  the  pieces  should  be  large  rather  than 
small;  (2)  the  boiling  should  be  rapid  in  order  to 
give  less  time  for  the  solvent  action  of  the  water 
to  act  upon  the  food  ingredients;  (3)  as  little  water 
as  possible  should  be  used;  and  (4)  if  the  matter 
extracted  be  used  as  food  along  with  the  carrots, 
instead  of  being  thrown  away,  the  loss  of  20  to  30 
per  cent,  or  even  more,  of  the  total  food  value  may 
be  prevented. 

EXPERIMENTS   WITH   CABBAGE. 


Experiments  analogous  to  those  with  potatoes 
and  carrots  were  made  with  cabbage  to  determine 
the  loss  of  food  material  during  the  process  of 
preparation  for  the  table. 

Cabbage  may  be  taken  as  representing  the  class 
of  pot  herbs  in  which  the  leaves  are  the  edible  por- 
tion. It  exposes  more  surface  to  the  action  of  the 
water  than  do  tubers  or  roots. 

COMPOSITION   OF   CABBAGE. 

The  composition  of  the  cabbage  analyzed  in 
connection  with  these  experiments,  as  well  as  the 
average  of  American  analyses  of  cabbage,  is  as 
follows : 

Composition  of  cabbage. 


PlG.  5. — The  composition  of 
the  carrot  and  the  loss  of 
nutrients  when  boiled :  a, 
fiber,  starch,  fat.  etc.:  b, 
sugar;  c,  nonalbuminoid 
nitrogenous  matter;  d, 
albuminoid  nitrogenous 
matter:  e,  mineral  mat- 
ter. The  hatched  portion 
represents  the  loss  when 
medium-sized  pieces  were 
boiled. 


Water. 


Albu- 
minoid 
nitro- 
gen. 


Total 
nitro- 
gen. 


Pro- 
tein. 


Fat. 


Carbohy- 
drates"'. 


Ash. 


Cabbage  used  in  these  experiments 

Average  of  7  American  analyses  a 


Per  ct. 
92.5 
90.3 


Per  ct. 
0.11 


Per  ct. 
0.18 


Per  ct. 

1.1 

•J.  1 


Per  ct. 
0.5 

.4 


Per  ct. 

o.T 
5.8 


Per  ct. 

0.7 
1.4 


all.  S.  Dept.  Agr.,  Office  of  Experiment  Stations  Bui.  28. 

2103—^0.  43 2 


is 
It  will   i»c  noticed   especially  that  in   cabbage  there  Is,  relatively, 

much  more  albuminoid    material  than  in  either  potatoes  Or  carrots,  the 

albuminoid  nitrogen  amounting  t<>  61  per  cent  of  the  total  nitrogen. 


COOKING    i  l> 

The  plan  of  the  experiments  was  the  same  as  that  followed  in  the 
experiments  with  potatoes  and  carrots.  In  each  trial  half  of  a  solid 
fair-sized  cabbage  was  used.  The  cabbage  was  boiled  in  a  metal  kettle 
over  a  g;is  flame  at  aboul  the  same  rate  as  on  an  ordinary  cook  stove. 
The  following  table  shows  t  he  results  obtained  by  I  he  different  methods 
of  cooking: 

odbbagi . 


1 

| 

-f 

;    i. 
Ti 

"8 

of  matter  in  In  >li 

cabc 

stituent. 

(   oil 

Method  of  cooking. 

_ 

C' 
- 

|s 

< 

C 
B 

"3 

1 
H 

: 
u 

- 

- 

i 

-. 

E 

■- 
Q 

s  = 

-  - 

—  -.i 

|| 

-■- 

P.et. 
2.7 

8.2 

| 

'= 
a 

1  at  and  .  ,ii  1... 

< 

Distilled  water,  cold  at  stai  t 
Do 

iirti  ma. 
471.7 
390. 1 

P.Ct.     J'.rt. 

2   I-    0.003 

2.  09      .  1109 

P.et. 
0.062 

J'.rt. 
1.7G 
2.01 

P.et. 

0.33 
.34 

p.* 

:;:;.  2 
36. 0 

P.et.    P.et. 
31.1 

30.  G 

P.et. 

47.1 

2.  68      .  (JOG      .  058 

1.88 

.34 

34.  6 

12.4 
41.2 

5.  5      32.  5      33.  3 

47.8 

8.2 
11.8 

Alkaline  water,  cold  at  start. 
Do 

317.5 

3.17     .009 

3.08      .013 

.081 

.065 

2.37 

.27 
.30 

45.  0     42.  3 
36.  1 

::s  t; 

3.12      .011      .073     2.38 

.  29 

41.8 

10.  (I     40.  G     42. 1 

40.7 

Limewater,  cold  at  start 

Do 

331.  1 
240.4 

3.17     .005 
3.05    

.087     2.23 
.078     2.20 

.40 

42.4 

l".  - 

4.  6      48.  3 

4:;.:; 

57.1 

51.4 

Average 

3.11 

.005 

.  083     2. 22 

.38 

41.6 

4.6     45.8     39.2 

54.  2 

Average  of  6  te>t>  in 

39.3 

6.  7     39.  o 

47.6 

Distilled  water,  hoi  at  start  . 

Do 

435.5 
387.  4 

2.  17      .  005 

2. 22      .  008 

.060 
.054 

1.56 

1.65 

.23 
.23 

29.0 

2.  20      .  007      .  05' 

.23 

29.4 

6.0      31.7      28.4 

32.  9 



iii_ 

317.5 

'263.  1 

2.  79 

Alkaline  water,  hot  at  start.. 
Do 

.057     2.13 

.  013      .  070     2.  04 

.21 

.27 

36.1 

37.3 

11.  s 

31.7      37.7 
36.1 

30  0 

A  rerage  



2.75     .011     .067     2.09 

.24 

36.7 

!■.  G 

37.  0     36.  9 

34.3 

Limewater,  hot  at  start 

Do 

689.  5 

3.05      .006     .071      2.21 
_  32    068     2.04 

.-in      40.8 
.35 

39.  4     39. 1 
37.  -     36  1 

57.  1 
5  1.  0 

a \  erage  

2.94      .006      .070      2.12 

.38 

5.  5     38.  6     37.  G 

53.5 

Average  of  G  testa  in 

35.1 

7  o     ::"»  «     34.3 

in.  2 

Even  under  the  most  favorable  conditions  the  loss  during  the  cook- 
ing of  Cabbage  is  very  great,  being  30  per  cent  of  the  total  dry  matter 
when  distilled  water  is  used  and  as  high  as  In  per  cent  when  lime- 
water  is  used.  In  the  latter  case  over  one  half  of  the  mineral  matter 
and  over  one  third  each  of  the  carbohydrates  and  nitrogenous  matter  are 
dissolved  oul  during  the  process  of  cooking.     The  albuminoid  matter 


19 


seems  to  be  less  soluble  than  any  other  of  tin-  substances  present,  there 
being  but  from  5  to  10  per  cent  of  loss.  Since  albuminoids  make  up 
01  per  cent  of  the  total  nitrogenous  substances,  it  follows  that  with  a 
loss  of  from  3j  to  10  percent  of  the  total  nitrogenous  matter  nearly  all 
of  the  nonalbuminoid  nitrogenous  compounds  must  be  dissolved  out  in 
the  water  m  which  the  cabbage  is  cooked.  It  will  be  noticed  that  the 
loss  of  albuminoid  nitrogen  was  much  greater  where  alkaline  water 
was  used  than  with  either 
distilled  or  lime  water.  The 
average  loss  in  the  cooking 
of  cabbage  is  shown  graph- 
ically in  tig.  0. 

CONCLUSIONS. 

The  kind  of  water  used  has 
more  effect  on  the  loss  of 
nutrients  in  cooking  cab- 
bage than  the  temperature 
of  the  water  at  which  the 
cooking  is  started.  In  any 
case  the  loss  is  large.  In  100 
pounds  ofuncooked  cabbage 
there  are  but  Ih  pounds  of 
dry  matter,  and  of  this  dry 
matter  from  2J  to  3  pounds 
are  lost  in  the  process  of 
cooking.     This  loss  seems  to 

be  unavoidable  unless  the  cabbage  is  cooked  in  such  a  manner  that 
the  water  in  which  it  is  boiled  is  also  used.  This  is  frequently  the 
case  when  cabbage  is  cooked  with  corned  beef. 

GENERAL   SUMMARY. 

The  losses  which  occur  in  cooking  potatoes,  carrots,  aud  cabbage 
vary  with  the  different  methods  of  boiling  followed,  being  quite  con- 
siderable in  some  cases.  These  losses  must  be  taken  into  account  in 
computing  dietaries  and  made  good  by  adding  other  materials  to  sup- 
ply the  nutrients  lost.  While  the  loss  is  not  so  great  as  to  render 
it  imperative  that  people  in  comfortable  circumstances  should  aban- 
don methods  of  preparing  these  foods  which  they  consider  make  them 
most  palatable,  there  are  very  large  numbers  who  can  not  afford  to 
permit  even  the  comparatively  small  waste  of  food  observed  in  these 
experimeuts. 

The  purpose  of  experiments,  such  as  those  here  reported,  is  to  learn 
what  actually  takes  place  in  the  process  of  preparing  food  by  the  com 
raon  methods.    Those  having  charge  of  the  preparation  of  food  must 
determine  how  far  it  is  desirable  under  individual  circumstances  to 
apply  the  information  obtained. 


Fig.  6.— The  composition  of  the  cabhage  and  the  loss  of 
nutrients  when  boiled:  o,  starch,  sugar,  fiber,  fat,  etc.; 
b,  nonalbuminoid  nitrogenous  matter;  c,  albuminoid 
nitrogenous  matter;  d,  mineral  matter.  The  hatched 
portion  represents  the  loss. 


THE  DIGESTIBILITY  OF  POTATOES  AND  EGGS. 

By  H.  8m  deb,  r>.  8., 

Chemist,  Minnesota  Agricultural  Experiment  station,  and  Professorof  Agricultural 
ChemistrUf  College  of  Agriculture^  University  of  Minnesota. 

INTRODUCTION. 

There  seems  to  be  a  very  wide  difference  of  opinion  regarding  the 
digestibility  of  the  potato,  some  considering  it  a  very  easily  digested 

food  and  others  a  food  digested  with  sonic  difficulty.  The  Information 
on  which  such  opinions  arc  based  is  comparatively  limited.  Our  knowl- 
edge concerning  the  digestibility  of  food  is  qnite  largely  based  on  artifi- 
cial digestion  experiments.  The  number  of  experiments  made  with  man 
is  comparatively  small.  An  experiment  with  man  on  the  digestibility 
of  potatoes  was  made  by  Rubner  and  reported  some  years  ago.1 

More  work  of  this  nature  seemed  desirable,  therefore  an  experiment 
was  undertaken  with  a  healthy  man  in  which  potatoes  formed  the 
principal  article  of  diet.  Potatoes  being  almost  entirely  a  farinaceous 
food,  it  was  necessary  to  have  some  easily  digested  albuminoids  in  the 
dietary  and  also  some  fat,  since  previous  digestion  experiments  in  this 
laboratory  have  indicated  that  in  order  to  obtain  normal  digestion  it  is 
necessary  to  use  a  well-balanced  ration  supplying  a  sufficient  amount 
of  nitrogenous  material  for  replenishing  the  waste  tissues  of  the  body. 
To  furnish  this  nitrogenous  matter  and  fat  hard-boiled  eggs  were 
added.  Upon  trial  the  diet  of  potatoes  and  eggs  proved  an  unnatural 
and  distasteful  one  to  the  subject  and  it  was  found  necessary  to  add 
some  milk  and  a  little  cream  to  the  dietary  in  order  to  make  it  well 
balanced  and  palatable. 

The  digestibility  of  the  eggs  was  first  determined  by  the  Stutzer 
method  of  artificial  digestion,  to  learn  something  of  the  effect  of  boil- 
ing for  various  periods.  Such  knowledge  was  considered  essential  in 
the  interpretation  of  the  results  of  the  experiments  with  man.  The 
digestibility  of  the  milk  and  cream  were  assumed  as  described  beyond. 

DIGESTIBILITY   OF   BOILED   EGGS  IN   PEPSIN   SOLUTION. 

Five  experiments  were  made  to  determine  the  digestibility  of  eggs 
cooked  under  different  conditions.  A  pepsin  solution  was  prepared 
consisting  of  1.1  parts  of  pepsin  and  7..">  parts  of  hydrochloric  acid  in 


■Ztschr.  Biol.,  1879,  p.  147.     U.  8.  Dept.  Agr.,  Office  of  Experiment  Stations  Hoi. 
21,  i».  tic 
20 


21 

500  parts  of  water.  This  solution  dissolved  50  parts  of  hard-boiled 
egg  albumen  in  six  and  one-half  hours  at  a  temperature  of  from  38° 
to  40°  0. 

Eggs  were  cooked  for  3  minutes  at  100°  0.,  giving  a4'  soft-boiled  "egg, 
and  for  5  minutes  and  _J0  minutes  at  the  same  temperature.  One  egg 
boiled  3  minutes  and  digested  for  5  hours  in  about  200  cc.  of  pepsin 
solution  as  prepared  above,  compared  with  one  boiled  20  minutes  and 
treated  in  the  same  way,  showed  8.3  per  cent  undigested  nitrogen  in 
the  former,  against  4.1  per  cent  undigested  nitrogen  in  the  latter. 
Under  similar  treatment  the  egg  boiled  5  minutes  gave  3.9  per  cent 
undigested  nitrogen. 

Another  trial  was  then  made,  in  which  the  eggs  were  cooked  for 
periods  of  5  and  10  minutes  in  water  at  82.2°  C.  (180°  F.)  In  both  of 
these  cases  the  nitrogen  was  entirely  digested  in  5  hours.  The  results 
are  given  in  the  following  table: 


Evsult  of  digesting 

boiled  eggs  5  hours 

in  pe2)sin  solution. 

No.  of 
experi- 
ment. 

Length 
of  time 
cooked. 

Tempera- 
ture at 
which 
cooked. 

Weight 

egg  used 

(without 

shell) . 

Grams. 
39.34 
47.02 
38.67 
43.  80 
40.64 

Total 
nitrogen 
in  fresh 

eggs. 

as  i  rai 

gested      ^rogen 
nftrogen.  dlSested- 

Pepsin 

solution 

used. 

1 
2 
3 
4 
5 

Mi Date*. 

5 

10 

3 

5 

20 

Beg.  F. 
180 
180 
212 
212 
212 

Grams. 

.944 
1.128 

.929 
1.050 

.960 

Grams. 

Per  cent. 

100.0 

100.0 

91.7 

96.1 

95.8 

Cc. 
197 
235 
193 
219 
203 

0. 0768 
.0408 
.0408 

From  the  above  it  seems  probable  that  while  the  method  of  cooking 
has  some  effect  upon  the  rate  of  digestibility  it  does  not  materially 
affect  the  total  digestibility.  These  results  agree  quite  closely  with 
those  obtained  by  Kubner.1  In  an  experiment  with  man  he  found  that 
97.1  per  cent  of  the  nitrogen  of  hard-boiled  eggs  was  digested. 

DIGESTION  EXPERIMENT  ON  MAN  WITH  A  DIET  OF  POTATOES,  EGGS, 

MILK,  AND   CREAM. 

The  subject  of  the  digestion  experiment  was  a  healthy  man,  22  years 
old.  He  was  a  laboratory  assistant,  and  his  work  did  not  demand  a 
great  amount  of  muscular  exercise.  The  experiment  began  with  dinner 
May  14,  1896,  and  ended  after  dinner  May  18,  covering  13  meals,  or  4.\ 
days.  The  weight  of  the  subject  (without  clothing)  at  the  beginning 
of  the  experiment  was  62.5  kilograms  (137J  pounds)  and  at  the  end 
62.0  kilograms  (137J  pounds). 

The  daily  dietary  as  finally  adopted  consisted  of  1587.6  grams  (3 J 
pounds)  of  potatoes,  8  eggs,  710  cubic  centimeters  (1J  pints)  of  milk, 
and  237  cubic  centimeters  (J  pint)  of  cream.  The  latter  was  necessary 
in  order  to  supply  fat  to  raise  the  fuel  value  of  the  food  to  the  desired 


^tschr.  Biol.,  1.879,  p.  128.     U.  S.  Dept.  Agr.,  Office  of  Experiment  Stations  Bui. 
21,  p.  61. 


22 


point.    The  approximate  amounts  and  the  composition  of  each  food 
consumed  per  day  are  shown  in  the  following  table: 


Amount  mill  <  om  /nisi  I  ion  oj'  pit  I  i  in  i  no  i  1/  daily  dirt. 


Solid 

matter. 


•  ii     Protein. 


<';irl)0- 


Pnel 
value. 


Qrams.      Oranu  Grams.  \  i 

Potato  id,! 

-    hard  boiled)    n  B   16  

Milk  (710  cubic  centimeters)  w.  72  25.4(1  27.  22 

Cream  (237  cubiccentimeters)  1  .91 


Total 


19.50 


121.56         110.  ( 


This  diet  was  given  for  three  days  before  the  experiment  began  in 
order  that  the  body  might  gel  into  equilibrium  with  it. 

After  breakfast  on  the  day  the  experiment  commenced  and  alter  din- 
ner on  the  day  it  closed  some  charcoal  in  gelatin  capsules  was  taken, 
in  order  to  identify  the  feces  belonging  to  the  food  of  the  experiment 
proper.  The  fresh  \\^'v>  weighed  on  an  average  204  grams  per  day  and 
the  mine  1,108  grams.  The  food,  urine,  and  feces  were  analyzed.  The 
composition  of  the  total  food  eaten  and  of  the  total  feces,  together  with 
the  nutrients  contained  in  the  food  eaten  and  lost  in  the  feces  and  the 
percentage  of  each  nutrient  digested,  are  shown  in  the  following  tables: 

Weight  and  composition  of  food  oaten  and  of  feces  for  font  and  one-third  days. 


Weight. 

TotaJ 
organic 
matter. 

Protein. 

Fat 

Carbohy- 

Ash. 

Foe! 
value 

per 
gram, 
calcu- 
lated. 

Grams. 

<     - 
1,800 

•_'.  722 

«206 

28.  85 
23.  86 
L2.27 
17.41 
82.  33 

/".  r  '■-  nt. 
9.50 

12.63 
::.  25 
1.69 

26.56 

0.08 
11.23 

4.01 
14.00 

14.30 

19.27 

P<  ;■  Ci  nt. 

0.90 
.86 
.75 

16.27 

0.935 

Milk 

5.01 
1.72 

Ml.  47 

1. 166 

a  Water-free  substance. 

Mhir  and  four  tenths  per  cent  is  allowed  for  biliary  products.    <  arbohj  drates      100.00     <• Protein  + 
Fat      Ash +  1.40). 

Weights  and  fuel  values  of  nutrients  in  food  eaten  and  in  feces  for  four  and  one-third 
days:  and  weights,  fuel  value,  and  percentages  of  nutrients  digested. 


Total 
organic 
matter. 

Protein. 

Fat. 

Carbohy- 
drates. 

Ash. 

Fuel 
value. 

Grams. 
1,394.0 

drams. 
159.5 

Grams. 

.">.  1 

Grams. 

drams.      Col 

."■7.  J 

E«rrrS 

420.  5            227!  4 
334.  0            88. 5 
158.0             15.3 

202.  1 



l(i  f. 

Milk       

109. 1 
127.  1 

136.4 

15.  (i 

" 

Total  egga,  milk,  and  cream 

921.5            3:U.2 

438.  3 

152.0 

4-J.  3 

6,  520 

Total,  from  whole  food 

2,315  5           490.7 

443.4 

1,381.4 

09.  7 

12  106 

Feces,  i.  e.,  undigested  residue 

Amount  digested  in  whole  food 

L69.9 

2,  11"..  6 

1           321   2 

413.9 

1,295.8 
L52.0 

1.  14::.  8 

I 

66.  1 

1 

11,  ISO 
0.  192 

• 
02.7             88.8 

'in    1; 

1 

ivic.ni  digested  of  pot. not- 

8 An  unknown  amount   of  salt   was  eaten,  which  renders  the  amount   ol    mineral  matter  ilij 
soin.u  hat  doubtful 


2:\ 

In  calculating  the  amount  of  nutrients  furnished  by  the  eggs,  milk, 
and  cream  that  were  digested,  it  is  assumed  that  97  per  cent  of  the 
protein  and  all  of  the  carbohydrates  (chiefly  milk  sugar)  in  these  foods 
were  digested.  Inasmuch  ;is  the  amount  of  fat  in  the  potato  is  bo 
extremely  small,  no  attempt  was  made  to  calculate4  its  digestibility. 
The  figures  for  the  digestibility  of  the  whole  food  (93  per  cent)  practi- 
cally represent  the  digestibility  of  the  fat  in  the  eggs,  milk,  and  cream. 
The  amount  of  nutrients  digested  in  the  eggs,  milk,  and  cream 
deducted  from  the  total  digested  nutrients  gives  the  nutrients  digested 
from  the  potato.  The  percentages  digested  were  calculated  from  these 
amounts.  In  calculating  the  fuel  value  1  gram  of  protein  is  assumed 
to  yield  5.5  calories.  1  gram  of  fat  9.3  calories,  and  1  gram  of  carbohy- 
drates 4.1  calories.  Nitrogenous  matter  is  not  as  completely  oxidized 
iu  the  body  as  when  burned  in  the  air,1  since  it  is  largely  excreted  in  the 
form  of  urea.  Urea  contains  some  energy,  which  is,  however,  unavail- 
able to  the  body.  Briefly,  the  fuel  value  of  urea  is  calculated  as 
follows:-' 

M  protein 

X  2.143  x  2.53=fuel  value  of  urea. 

r,.i>5 

This  may  be  reduced  to  the  simpler  form,  M  protein  x  0.87= fuel 
value  of  urea. 

More  or  less  salt  was  eaten  of  which  no  account  was  made,  therefore 
the  digestibility  of  the  ash  is  not  calculated.  It  is  of  comparatively 
little  importance,  since  to  some  extent  at  least  the  soluble  mineral 
matters,  e.  g.,  salt,  pass  directly  to  the  kidneys,  from  which  they  may 
be  secreted  within  a  few  hours  after  being  taken  into  the  stomach. 

DISCUSSION   OF   RESULTS. 

From  the  results  of  this  experiment  it  would  seem  that  while  the 
nitrogenous  matter  is  not  very  completely  digested,  the  digestibility  of 
the  carbohydrates  is  quite  high.  Since  the  potato  consists  very  largely 
of  carbohydrates,  it  may  be  regarded,  at  least  in  the  case  of  the  per- 
son here  experimented  with,  as  a  food  which  is  well  digested.  The 
results  obtained  in  this  experiment  agree  very  closely  with  those 
obtained  by  Rubner  (see  p.  21),  as  will  be  seen  by  the  following  com- 
parison: 

The  digestibility  of  potatoes  as  determined  by  American  and  European  investigators. 

I  Protein  l0^?^ 


.Percent.    Percent. 

The  authors  experiment I  71.  9  93.0 

Rnbner's  experiment 67.  8  i  92. 4 


JU.  S.  Dept.  Agr.,  Office  of  Experiment  Stations  Bui.  21,  p.  103. 
"Connecticut  Storrs  Sta.  Rpt.  1894,  p.  125. 


24 

The  nitrogen  balance. — The  urine  was  collected  daring  the  period  cov- 
ered i»>  the  digestion  experiment,  and  the  total  <>i  solids,  nitrogen,  and 
ash  in  it  determined.  In  tins  way  a  balance  of  income  and  outgo  of 
nitrogen  could  be  obtained  and  the  resultant  gain  or  loss  of  protein 
calculated.  The  amount  of  urine  excreted  during  the  period  covered 
by  the  experiment  was  1,800  grams.  Ii  contained  6.18  per  cent  of 
water  free  substance,  1.42  percent  of  nitrogen,  and  1.63  per  cent  of  ash. 
The  gain  <>r  loss  of  nitrogen  ;m<l  the  calculated  gain  or  loss  of  protein 
per  day  are  shown  in  the  following  table: 

BaJat  //*'  anil  outgo  of  nitro fn  and  gain  of  protein. 


S'itrogeu     P 
in  food,     in  g   -t«-<l.    in  urine.     .  ;  lined. 


Qnantitiefl  t'<>r  \\  hole  \n a 

Quantities  per  da; , — 


i 

18.14 


<i  rains. 
16.11  15.74 


.VI 


9.88 


During  the  experiment  the  subject  gained  9.88  .mam-    one  third  of 
an  ounce  of  protein.     Assuming  that  muscle  contained  23  percent  of 

protein,  the  subject  gained  43  grams  of  muscle,  or  about  1£  ounces. 


THE  COMPOSITION  OF   DIFFERENT  PARTS   OF  THE   POTATO   AND 
THE  LOSS  OF  NUTRIENTS  DURING  THE  PROCESS  OF  BOILING. 

By  Almaii   J.    Prisby,   M.    1>.,  and  A.    P.    BRYANT,   M.   S. 
INTRODUCTION. 

The  potato  is  composed  of  three  parts,  which  may  for  convenience  be 
termed  outer  skin,  inner  skin,  and  flesh.  The  outer  or  true  skin  is  dry 
in  appearance,  usually  grayish  brown  in  color  and  corresponds  to  the 
bark  of  the  rest  of  the  plant.  The  portion  lying  immediately  beneath 
the  skin  is  slightly  colored,  containing  whatever  coloring  matter  may 
be  present  in  the  potato,  and  is  the  part  which  turns  green  on  continued 


Fig.  7.— Transverse  and  longitudinal  sections  of  the  potato  (after  Condon  and  Bussard) 
b,  cortical  layer ;  c,  outer  medullary  layer;  d,  inner  medullary  layer. 


skin; 


exposure  to  the  sunlight,  giving  a  strong  unpleasant  taste  to  the  potato. 
This  portion  has  some  resemblance  to  the  skin  in  general  appearance, 
and  is  usually  removed  with  the  skin  in  preparing  potatoes  for  the 
table.  Its  true  name  is  the  flbro-vascular  layer,  but  it  is  also  some- 
times designated  as  the  herbaceous  or  cortical  layer,  subcutaneous  por- 
tion, and  inner  skin  (see  fig.  7 ).    The  main  bulk  of  the  potato  is  composed 

25 


26 

filled  with  starch  grains  and  a  Little  nitrogenous  matter,  and  may  be 
designated  as  the  flesh  of  t he  potato. 

[Shortly  after  the  completion  of  the  present  bulletin  an  extended 
study  of  potatoes  was  reported  l>\  B.  Ooudon  and  L.  Bussard.1  The 
authors  Investigated  the  botanical  structure  of  a  large  number  of  vari- 
eties of  potatoes  and  determined  the  relative  composition  of  large, 
medium,  and  small  potatoes  and  of  the  different  parts  of  the  tubers. 
The  taste  and  culinary  properties  of  a  number  of  standard  varieties 
were  also  investigated.    The  potatoes  were  cooked  in  several  ways. 

Anions  the  Conclusions  reached  by  the  authors  were  the  following:   In 

judging  the  value  of  a  variety  of  potatoes  analyses  should  be  made  of  a 
number  of  entire  tubers.  The  culinary  value  of  the  potato  is  directly 
proportional  to  its  nitrogen  content  and  inversely  proportional  to  its 
starch  content.  The  different  varieties  of  potatoes  were  found  to  vary 
greatly  in  their  resistance  to  boiling,  some  retaining  their  form  com- 
pletely, while  others  were  almost  entirely  disintegrated.  In  the 
author's  opinion  the  resistance  to  boiling  did  not  depend  upon  the  con- 
tent of  pectin  or  starch,  but  seemed  to  depend  principally  upon  the 
relative  proportion  of  albuminoids  present.'  No  definite  relation  was 
observed  between  chemical  composition  and  early  maturity.  <  renerally 
speaking,  the  early  varieties  contained  more  water  and  nitrogenous 
material  and  less  starch  than  the  late  varieties.  The  number  of  excep- 
tions was,  however,  large.  | 

In  order  to  ascertain  to  some  extent  the  variation  in  composition  of 
the  different  parts  of  the  tuber  a  quantity  of  smooth  potatoes  of  aver 
age  size  was  obtained  and  analyses  of  the  different  parts  made.     The 
variety  selected  was  that  known  as  the  "White  Star." 

COMPOSITION   OF   DIFFERENT   PARTS  OF  THE   POTATO. 
SAMPLING. 

Twelve  medium-sized  potatoes  of  known  weight  were  taken.  The 
skin  was  carefully  removed  by  scraping  with  a  knife  and  the  skin  and 
potatoes  weighed.  The  sum  of  the  weights  of  the  scraped  potatoes 
and  of  the  skins  did  not  equal  the  weight  of  the  potatoes  at  the  start. 
More  or  less  water  had  evaporated  from  the  moist  surfaces.  It  was 
assumed  that  half  of  the  loss  came  from  the  skins  and  half  from  the 
smooth  surface  of  the  scraped  potatoes,  inasmuch  as  the  amount  of 
surface  freshly  exposed  to  the  air  was  the  same  in  the  two  portions. 
'fhe  inner  skin  of  the  potatoes,  or  libro  vascular  layer,  was  next 
removed  by  scraping,  care  being  taken  to  include  as  little  flesh  of  the 
potato  as  possible.  The  amount  removed  by  this  operation  was  weighed 
as  before  and  the  loss  of  water  during  the  process  divided  equally 
between  the  part  removed  and  the  part  remaining,  i.  e..  the  flesh.  The 
three  portions  were  dried  at  LOO    ('.and  this  partially  dried  material 


1  Ann.  8ci.  Agron..  L897,  I.  No. 2,  p. 250. 


27 

of  cells  was  analyzed.    The  weights  of  the  different  parts  and  their 

proportion  of  the  whole  potato  were  as  follows: 

Proportions  of  different  purls  of  the  potato. 


Twelve  un  peeled  potatoes 

Outer,  or  true    skin 

Inner  skin  or  libro- vascular  Layer  a. 
Flesh 


Weighl      Percenl 
in  grams,  of  whole. 


1,633 

41 
139 

1,453 


100.0 
2.5 
8.5 
80.0 


a  Encluding  a  small  amount  of  tlosli. 


THE    ANALYSES. 


Water,  nitrogen,  fat,  and  ash  were  determined  by  the  usual  methods. 
Crude  fiber  was  determined  in  the  fibro-vaseular  layer  and  the  flesh, 
but  there  was  so  little  of  the  skin  left  after  making  the  other  deter- 
minations that  the  estimation  of  liber  could  not  be  made.  It  would, 
however,  presumably  be  quite  high. 

The  nitrogen  of  the  potato  is  not  all  in  the  form  of  true  albuminoids 
or  proteids,  but  nearly  half  is  in  the  form  of  amido  compounds,  includ- 
ing, principally,  asparagin.1  Inasmuch  as  the  amount  of  nitrogenous 
material  in  the  potato  is  small,  and  the  amido  compounds  can  neither 
build  tissue  nor  repair  waste  as  do  the  albuminoids,  the  nutritive 
value  of  the  nitrogenous  substance  (protein)  of  the  potato  is  very  small. 
In  the  experiments  here  reported  the  albuminoid  nitrogen  was  deter- 
mined by  Stutzer's  method. 

The  composition  of  different  parts  and  the  calculated  composition  of 
whole  potatoes  here  analyzed  as  compared  with  results  of  other  Ameri- 
can and  European  analyses  are  shown  in  the  following  table: 

Composition  of  the  ichole  potato  and  its  different  parts. 


Outer,  or  trno,  skin 

Inner  skin  or  fibro-vaseular  layer. 

Flesh 

Calculated  composition  of    whole 

potato 

Average  of  86  American  analyses  a 
Average  of  1 78  European  analyses  h 


Nitrogen. 


Water. 


Per  ct. 
80.1 
8*.  2 

81.1 

81.3 
78.0 
75.0 


Albu- 
minoid. 


Total. 


Pro- 
tein. 


Fer  ct. 

0.25 

.24 

.18 


Per  ct.  I'i  r  rt. 

0.43  2.7 

.36  2. 3 

.32  2. 0 


.32 
.35 
.34 


2.0 
2.2 
2.1 


Carbohydrates. 


Fat. 


Nitro-  | 
gen-free   Fiber, 
extract. 


Per  ct. 

0.8 
.1 
.1 

.1 
.1 
.1 


0. 


Per  ct.     Per  ct. 
•       14.6 
12.6  I 
15.7 

15.7 
18.8 
21.0 


Ash. 


Per  ct. 

1.8 


1.1 


.9 
1.1 


a  From  an  unpublished  compilation  of  analyses  of  American  food  products. 
frKonig,  Chemie  der  Nahrungs-  and  Gennssmittel,  3d  ed.,  II.  p.  626. 

Although  of  tine  appearance,  the  potatoes  used  in  the  present  experi- 
ment contained  au  unusually  small  amount  of  dry  matter  and  a  large 
proportion  of  water,  as  will  be  seen  by  comparing  their  chemical  com- 

1  Sclmlze,  Larbieri,  and  Eugster,  Land.  Vers.  Stat.,  21  (1878),  p.  63;  27  (1882),  p.  357. 
See  also  Konig,  Chemie  der  menschlichen  Xahrungs-  und  Genussmittel,  3d  ed.,  II, 
p.  631. 


28 

position  with  that  of  average  potatoes.  Whether  this  was  due  to  the 
variety  or  to  the  year  is  a  matter  of  doubt  The  skin,  although  appar- 
ently very  dry,  contained  nearly  as  large  a  percentage  of  water  as  the 
pest  of  the  potato.  The  portion  immediately  under  the  true  skin,  i.  e., 
the  flbrp-vascular  layer,  contained  the  .greatest  amount  of  water. 
Pay  en1  states  that  the  epidermis  and  the  herbaceous  portion  imine 
diatcly  l»elow  it  contain  little  or  no  starch  deposit.  The  above  results 
seem  to  be  in  accord  wit  1 1  this,  though  DO  «'stiinat  i<>n  of  starch  itself 
was  made.  It  will  be  noticed  that  tin*  skin  contains  about  10  per  cent 
more  albuminoid  nitrogen  than  the  llesh.  and  more  than  twice  the 
amount  of  mineral  matter  ash).  One  of  the  most  noticeable  differ- 
ences is  the  relatively  large  amount  of  ether  extract  in  the  skin — nearly 
1  per  cent.  This  had  much  the  appearance  of  wax,  and  had  an  odor 
slightly  resembling  that  of  beeswax. 

I  m:    PRO!  I'lN    FACTOR. 

The  protein  was  determined  as  usual  by  multiplying  the  total  nitro 
gen  by  the  factor  6.25.  This  factor  is  based  on  the  assumption  that 
there  is  on  the  average  L6  per  cent  of  nitrogen  in  protein.  In  the  case 
of  potatoes  the  results  thus  obtained  are  considerably  too  large.  In 
the  fust  place,  the  nonalbuminoid  compounds  have  a  much  larger 
proportion  of  nitrogen  than  do  the  albuminoids,  and  consequently 
should  be  obtained  by  the  use  of  a  much  smaller  factor  than  6.25. 
Besides  this,  the  albuminoids  themselves  contain  slightly  more  than 
Hi  per  cent  of  nitrogen.  Osborne  and  Campbell2  have  investigated  the 
proteid  of  the  potato,  which  they  propose  to  call  "tuberin,"  and  find 
that  it  contains  10.24  per  cent  of  nitrogen. 

For  the  present  purpose  it  will  be  convenient  to  assume  that  all  the 
nonalbuminoid  nitrogen  of  the  potato  occurs  in  forms  more  or  less  sim- 
ilar to  asparagin.  Asparagin  contains  21.21  per  cent  of  nitrogen.  The 
average  amount  of  albuminoid  nitrogen  in  potatoes  is  5(>  percent  of 
the  whole,  which  is  the  same  proportion  as  was  found  in  the  tlesh  of 
the  potatoes  used  in  these  experiments.  Assuming  56  per  cent  of  the 
nitrogen  of  the  potato  to  belong  to  albuminoid  nitrogenous  matter 
(tuberin)  and  the  remaining  44  per  cent  of  the  nitrogen  to  belong  to 
nonalbuminoid  nitrogenous  matter  (asparagin),  there  will  be  an  aver- 
age of  18.42  per  cent  of  nitrogen  in  the  nitrogenous  substance  of  the 
potato.    This  corresponds  to  the  factor  r>.43. 

In  round  numbers,  therefore.  5.5  may  be  taken  as  the  factor  by  which 
the  total  nitrogen  of  the  potato  should  be  multiplied  in  order  to  obtain 
the  total  nitrogenous  matter  or  protein.  While  the  change  made  by 
using  this  instead  of  the  ordinary  factor  6.25  for  calculating  the  protein 
is  slight,  it  would  amount  to  about  a  gram  of  protein  per  day  in  the 
ease  of  a   person  eating  old  grams  (f   pound)  of  potatoes  daily.     The 


Substances  alimeatairea,  p.  :;<>"'. 
'Connecticut  State  Sta.  Bpt.  L8953  p.  255  (E.S.R.,  8,  p.  371). 


29 

difference  in  composition  as  computed  by  using  the  factor  5.5  for  calcula  t 
ing  protein  instead  of  the  factor  G.25  is  shown  in  the  following  table: 

Comparison  of  the  composition  of  the  potato  when  the  factor  5.5  w  ueed  instead  of  the 
factor  6.25  in  calcula  ting  protein. 


Water. 

Protein. 

Fill. 

<  larbohydratee  by 
difference,  a 

Nitrogen 
5.5. 

Nitrogen 
X  6.25. 

When 
protein 

N     5.5. 

When 
protein 
x    6.25. 

Ash. 

Outer,  or  true,  skin 

[nner  skin  or  Bbro- vascular  laj  ei 
Flesh            

Per  ct. 

80.1 
83.2 
81.1 

81.3 
78.0 

Per  cent. 
2.4 
2.0 
1.8 

1.8 
1.9 

Per  cent, 

2.7 
2.3 

2.0 

2.0 
2.2 

l'errt. 

0.8 

.1 

.1 

.1 
.1 

Per  cent. 
14.9 
13.6 
16.2 

15.9 
19.1 

Per  cent. 
14.6 
13.3 
16.0 

15.7 
18.8 

Perct. 
1.8 
1.1 

.8 

Calculated   composition   of  whole 

.9 

Average  of  86  American  analyses. . 

.9 

a  100  less  the  sum  of  the  percentages  of  water,  protein,  fat,  and  ash. 


AMOUNT   OF    SOLID   MATTER   IN   THE   JUICE   OF   THE   POTATO. 

When  we  consider  the  amount  of  water  in  the  potato,  it  is  to  be 
expected  that  a  considerable  portion  of  the  ingredients  may  be  in  solu- 
tion. If  a  potato  be  grated  and  the  juice  pressed  through  a  linen  cloth 
a  large  amount  of  dark-colored  liquid  is  obtained  having  an  acid  char- 
acter. This  acidity  is  commonly  said  to  be  chiefly  due  to  citric  acid  with 
more  or  less  tartaric  and  succinic  acids.  The  mineral  water  is  very 
largely  in  the  form  of  potash  salts,  soluble  in  water.  The  asparagin 
present  is  also  soluble  in  water,  and  the  tuberin  more  or  less  soluble  in 
the  acid.  The  following  table  shows  the  percentages  of  the  different 
substances  found  in  the  juice  of  the  potato  and  in  the  solid  matter: 

Distribution  of  material  in  the  solid  matter  and  juice  of  the  potato,  a 


Dry 

matter. 

Nitrogen. 

Albumi-    Nonalbu- 
noid.        minoid. 

Albumi- 
noid + 

nonulbu- 
minoid. 

Ash. 

Per  cent. 
85 
15 

Per  cent.  Per  cent. 
15                  0 

Per  cent. 
15 

Percent. 
15 

49                36                85 

85 

Total 

100 

64                36 

100 

100 

a  Lawes  and  Gilbert,  On  the  Growth  of  the  Potato,  p.  26,  Eothamsted  Memoirs,  vol.  6. 
LOSS   OF  NUTRIENTS  IN  BOILING. 

Since  85  per  cent  of  the  nitrogenous  matter  and  85  per  cent  of  the 
mineral  matter  are  in  a  state  of  solution  in  the  potato,  it  would  seem 
quite  probable  that  there  might  be  a  considerable  loss  of  these  sub- 
stances during  the  process  of  preparing  potatoes  for  the  table.  Experi- 
ments were  therefore  made  to  investigate  this  loss  and  determine  its 


30 

amount.  Four  trials  wen-  made,  l  w  itli  the  -kins  removed,  the  peeled 
potatoes  being  i * 1 1 1  in  cold  water,  which  was  heated  at  oikt  over  a 
moderate  flame;  (2)  with  the  skins  removed,  the  peeled  potatoes  placed 

directly  in  boiling  water;   (3)  with  the  skins  on.  the  potatoes  being  put 
in  cold  water,  which  was  heated  as  in   the  firef   rase;   and  (4     with  the 
skins  (in.  tin-  potatoes  being  placed   directly  in  hot  water  as  in   tin 
ond  case.    Six  medinm  sized  potatoes  were  nsed  for  each  trial.    They 

were  boiled  in   one  liter  of  distilled  water  in  an    aluminum  kettle  until 

they  were  easily  pierced  with  a  fork.    The  kettle  was  then  removed 

from  the   tire,  the  water    poured  oil',  and   the   potatoes   linked  with   dis 

tilled  water.  It  was  found  that  the  potatoes  in  every  case  except  the 
second  gained  slightly  in  weight  during  tin*  process  of  cooking.  This 
gain  w  us  e\  idently  due  to  water  absorbed. 

The  water  in  which  the  potatoes  were  boiled,  united  with  that 
u>cd  in  rinsing  them  after  boiling,  was  made  up  to  a  definite  volume 
by  adding  distilled  water.  Aliquot  portions  were  taken  for  analysis. 
The  cooked  potatoes  were  also  dried  and  analyzed.  In  most  cases  the 
amount  of  each  substance  found  by  analysis  in  the  water  used  iu cook- 
ing them,  added  to  the  amount  of  the  same  substance  found  in  the 
cooked  potatoes,  gave,  within  the  limits  of  analytical  error,  the  total 
amount  of  that  substance  calculated  as  being  present  in  the  raw- 
potatoes.  The  weight  of  any  substance  found  in  the  water  used  in 
cooking  the  potatoes  divided  by  the  weight  of  that  same  substance 
calculated  as  being  present  in  the  uncooked  potatoes  gave  the  per- 
centage of  loss  during  boiling.  The  loss  of  carbohydrates  was  esti- 
mated by  subtracting  the  sum  of  the  protein  lost  calculated  by  multi- 
plying the  total  nitrogen  lost  by  5.5  and  the  mineral  matter  lost  from 
the  total  loss  of  dry  matter. 

The  following  table  gives  the  loss  of  nutrients  when  the  potatoes 
were  cooked  in  different  ways: 


The  loss  of  material  during  the  process  of  cooking  potatoes. 


Dry 

matter. 

Xiti 

Albumi- 
noid. 

Nonalbu-     ,..  ,  .         drates.         A>1' 
minoid.       lotal 

fort  boiting. 

Water  cold  ai  beginning  of  t.  si 

Water  hot  at  beginning  ol  teat 

3.7 
4.0 

3.3 

12.8 

17.  It              lO.d                                     17   J 

3.9 

15.4                                     -   7                17.2 

Baited  wit&  skim  on. 

..id  Mt  beginning  <>t'  teat 

Water  h"t  at                        teal 

.3 

.6 

.4 

.6                 .G                 .2                 1.9 
1.7               1.0                 .1                 I.  J 

1.1 


It  will  be  seen  that  the  loss  of  matter  during  the  process  of  cooking 
w  as  confined  quite  largely  to  the  oitrogenons  substances  and  the  min- 
eral matter.     The  total  loss  of  dry  matter,  however,  was  in  some  I 


31 

considerable,  indicating  a.  loss  of  starch  and  other  carbohydrates.  The 
loss  of  nitrogen  and  mineral  matter  is  easily  explained  by  supposing 

that  substances  which  were  dissolved  in  the  juices  simply  passed  <»ut 
into  the  water.  The  loss  of  the  carbohydrates,  <>n  the  other  hand,  is 
probably  largely  mechanical. 

It  Avill  be  noticed  that  the  calculated  loss  of  carbohydrates   was 

almost  nothing  when  the  potatoes  were  protected  by  their  skins. 
When  the  skins  were  removed  before  cooking,  more  or  less  of  the 
softened  and  broken  cell  walls  and  swollen  starch  grains  were  abraded 
during  the  process  of  boiling.  Although  this  process  is  mechanical, 
the  material  removed  is  just  as  truly  lost  as  if  an  equivalent  amount 
of  starch  had  been  converted  into  dextrin  during  the  boiling  and  then 
dissolved.  Possibly  there  is  a  slight  loss  of  starch  which  is  chemical 
rather  than  mechanical.  In  roots,  such  as  beets,  turnips,  and  carrots, 
there  is  more  or  less  sugar  which  might  dissolve  out,  but  the  fresh 
potato  contains  practically  no  sugar. 

CONCLUSIONS. 

When  potatoes  are  boiled  with  the  skins  removed,  there  is  a  very 
considerable  loss  not  only  of  organic  nutrients  but  also  of  mineral  salts. 
These  salts,  while  not  nutrients  in  the  sense  in  w  hich  this  term  is  fre- 
quently used,  are  nevertheless  important  in  nutrition.  They  are  of 
especial  value,  because  of  the  potassium  compounds  which  they  con- 
tain, and  are  apparently  necessary  for  health. 

The  greatest  actual  loss  of  nutrients  seems  to  be  due  to  the  mechan- 
ical abrasion  of  the  soft  outer  portions  of  the  potato  while  cooking. 
In  this  case  nearly  3  per  cent  of  the  carbohydrates  and  4  per  cent  of 
the  available  flesh-forming  nitrogenous  matter  are  lost.  When  the 
potatoes  are  boiled  with  their  skins  on,  the  loss  of  nutrients  is  very 
slight,  consisting  chiefly  of  nonalbuminoid  nitrogenous  substances  and 
mineral  matter.  It  is  self-evident  that  if  it  is  desired  to  boil  potatoes 
with  as  little  loss  as  possible  the  skins  should  be  left  on. 

O 


SSassn.  °<=  flor,da 

II  llll  III!  Ml 'ill 


3  1262  08927  7833 


i 


